The young striker, in his first start since picking up a hamstring injury against Arsenal in late August, scored twice to fire the Reds into an early 2-0 lead. But the Swiss visitors rallied to first equalise and then go ahead, before Ashley Young snatched a draw with a late header.
"To get two goals in the Champions League, I'm over the moon with that," Welbeck told Sky Sports. "But it's a team game and I'm disappointed.
"We went into half-time 2-0 up and Manchester United should be finishing teams off. It's just not like us [to let teams back into games].
"In the second half we didn't start as bright as we should have. They gradually worked their way into the game and pulled two goals back quickly."